Air conditioning system

ABSTRACT

Air conditioning system including an outdoor unit, a compact indoor unit, air supply duct, air discharge duct, and preheat exchanger. An indoor heat exchanger in the indoor unit has a space therein in communication with a room, a fan in the indoor unit provided in the space draws air and discharges through the indoor heat exchanger. A ventilation guide duct in the indoor unit on an underside of the indoor heat exchanger has a partition wall for separating external air supplied from an outside of the room, and room air, for guiding the external air to the room through the fan, and the room air to the outside of the room. The air supply duct and the air discharge duct have one ends connected to the ventilation guide duct for guiding the external air to the room, and the room air to the outside of the room, respectively. The preheat exchanger is provided in the middle of the air supply duct and the air discharge duct, for indirect heat exchange of the external air and the room air passing through the air supply duct and the air discharge duct.

[0001] This application claims the benefit of the Korean Application No.P2003-35982 filed on Jun. 4, 2003, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to air conditioning systems, andmore particularly, to an air conditioning system, in which an indoorunit installed on a ceiling, and a duct for ventilation are combinedinto one compact unit.

[0004] 2. Background of the Related Art

[0005] The air conditioner is an appliance for cooling or heating a roomby using a property of refrigerant in which the refrigerant dischargesor absorbs heat to/from an environment when the refrigerant undergoes aphase change.

[0006] In general, the air conditioner is provided with an indoor unitand an outdoor unit, wherein the air conditioner having the indoor unitand the outdoor unit combined into one unit is called as a unit type airconditioner, and the air conditioner having the indoor unit and theoutdoor unit fabricated individually is called as a separate type airconditioner.

[0007] As a typical example of the unit type air conditioner, there is awindow type air conditioner, and as the separate type air conditioners,there are a ceiling type air conditioner, a wall mounting type airconditioner, and a package type air conditioner. In a case of theceiling type air conditioner, the indoor unit is installed in theceiling, in a case of the wall mounting type, the indoor unit is mountedon a wall, and in a case of the package type air conditioner, the indoorunit stands on a floor in a room.

[0008] In general, the air conditioner includes a compressor, acondenser, an expansion device, and an evaporator. The compressorcompresses low temperature/low pressure gas refrigerant to hightemperature/high pressure refrigerant, and makes the refrigerant to passthrough different units. The condenser condenses the gas refrigerantfrom the compressor into a liquid refrigerant. In this instance, as therefrigerant discharges heat when the refrigerant is condensed, thecondenser discharges heat to an environment. As the heat is dischargedfrom the condenser to the room, the room can be heated.

[0009] In general, as the expansion device, expanding the condensedrefrigerant by decompression, capillary tubes are used. The evaporatorvaporizes the expanded refrigerant, when the refrigerant absorbs heat tocool down air around the evaporator. When such a cooled down air isdischarged to the room, the room can be cooled down.

[0010] In the meantime, for reducing heat loss during use of the airconditioner, the room is closed. Air in such a closed room is pollutedgradually as time passes by. For an example, breathing of persons in theroom makes a carbon dioxide content in the room air higher, and there ismuch dust circulating in the dry air. Therefore, after using the airconditioner for a time period, it is required to supply fresh externalair to the room. What is used for this is the very ventilation device.

[0011] Most of known related art ventilation device employs a system inwhich room air is only discharged to an outside of the room forcibly byusing a fan. In this case, it is required to leave the window open forventilation. However, when the room air is only discharged by one fanforcibly, cold or hot air is discharged to the outside directly, andexternal air is introduced into the room through an opened door orwindow, directly. Accordingly, there is a great loss of heat in theventilation, to require, not only much energy, but also a long time tocool or heat the room again.

[0012] Moreover, the sudden introduction of hot or cold air from theoutside to the inside of the room causes a sudden change of a roomtemperature, such that persons in the room feel unpleasant. Moreover,the opening of door or window without fail required when the ventilationdevice that discharges room air to outside of the room is in operationcauses inconvenience.

SUMMARY OF THE INVENTION

[0013] Accordingly, the present invention is directed to an airconditioning system that substantially obviates one or more of theproblems due to limitations and disadvantages of the related art.

[0014] An object of the present invention is to provide an improved airconditioning system which can recover heat from air discharged to anoutside of room during ventilation.

[0015] Another object of the present invention is to provide an improvedair conditioning system which can be installed more easily as duct forguiding ventilated air and an indoor unit combined into a compact unit.

[0016] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparent tothose having ordinary skill in the art upon examination of the followingor may be learned from practice of the invention. The objectives andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

[0017] To achieve these objects and other advantages and in accordancewith the purpose of the present invention, as embodied and broadlydescribed herein, the air conditioning system includes an outdoor unit,a compact indoor unit in a ceiling having a ventilation duct, air supplyducts, air discharge ducts, and preheat exchanger.

[0018] The outdoor unit includes a compressor and an outdoor heatexchanger, and the indoor unit includes an indoor heat exchanger, a fan,and the ventilation guide duct. The indoor heat exchanger has a spacetherein in communication with a room, the fan provided in the spacedraws air and discharges through the indoor heat exchanger. Theventilation guide duct on an underside of the indoor heat exchanger hasa partition wall for separating external air supplied from an outside ofthe room, and room air, for guiding the external air to the room throughthe fan, and the room air to the outside of the room.

[0019] The air supply duct and the air discharge duct have one endsconnected to the ventilation guide duct for guiding the external air tothe room, and the room air to the outside of the room, respectively. Thepreheat exchanger is provided in the middle of the air supply duct andthe air discharge duct, for indirect heat exchange of the external airand the room air passing through the air supply duct and the airdischarge duct.

[0020] The fan includes a centrifugal fan that draws air from under anddischarges in a radial direction as the fan rotates.

[0021] The ventilation guide duct includes a first flow passage incommunication with the space, the room, and the air supply duct, forguiding the room air and the external air to the fan, at least one ormore than one second flow passage for guiding the air passed through thefan and the indoor heat exchanger to the room, and a third flow passagefor guiding the room air to the air discharge duct.

[0022] The ventilation guide duct includes a duct body on an undersideof the indoor heat exchanger, and a panel attached to an underside ofthe duct body.

[0023] The duct body includes a first hole passed in an up/downdirection to form a part of the first flow passage and in communicationwith the air supply duct, a third hole passed in the up/down directionto form a part of the third flow passage, in communication with the airdischarge duct, and made independent from the first hole by thepartition wall, and a second hole passed in the up/down direction toform a part of the second flow passage.

[0024] The duct body includes first ducts arranged to surround a centralpart to form a cavity in the central part that is in communication withthe space and the room, each of the first ducts having an inside forminga part of the second flow passage, and the partition wall arranged todivide the cavity into the first flow passage and the third flowpassage. The partition wall has opposite two ends connected to oppositefirst ducts. The partition wall divides the cavity into two flowpassages having the same forms and sectional areas.

[0025] The duct body further includes connection plates connectedbetween side ends of adjacent first ducts, and the air supply duct orthe air discharge duct is connected thereto selectively.

[0026] The panel includes a first port formed to form parts of the firstand third flow passages, respectively, and a second port formed to forma part of the second flow passage. The panel may further include a meshprovided to the first port. The panel may further include a plurality oflouvers provided to the second port for guiding a discharge direction ofthe air passed through the indoor heat exchanger.

[0027] The fan is provided over the first hole and the third hole, andthe indoor heat exchanger stands on the duct body along positionsbetween the first hole and the second hole, and the first hole and thethird hole.

[0028] In the meantime, the preheat exchanger may include first guidepassages arranged at regular intervals for flow of the external airtherethrough, and second guide passages arranged to be in contactbetween the first guide passages for flow of the room air therethrough.The preheat exchanger includes a plurality of plates arranged at regularintervals so that the first guide passages for flow of the external airand the second guide passages for flow of the room air are formed inlayers, and a plurality of flow guides provided between the plates foreach of the layers in parallel to flow directions of the external airand the room air respectively, each having a cross section with aplurality of continuous folds. The fold includes a perk and a bottom incontact with a top surface and a bottom surface of the plates. The flowguides in each of the layers are arranged perpendicular to each othersuch that the external air and the room air flow in perpendicular toeach other.

[0029] The air conditioning system may further include an air supply fanmounted on the air supply duct for supplying the external air to theroom, and an air discharge fan mounted on the air discharge duct fordischarging the room air to the outside of the room. The air supply ductand the air discharge duct include at least one or more than one branchducts branched from one ends thereof and connected to the first flowpassage and the third flow passage.

[0030] It is to be understood that both the foregoing description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention claimed.

BRIEF DESCRITPION OF THE DRAWINGS

[0031] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this application, illustrate embodiment(s) of theinvention and together with the description serve to explain theprinciple of the invention. In the drawings;

[0032]FIG. 1 illustrates an air conditioning system in accordance with apreferred embodiment of the present invention, schematically;

[0033]FIG. 2 illustrates a view of the air conditioning system in FIG. 1installed on a ceiling looked up from below;

[0034]FIG. 3 illustrates heat exchange between external air and room airin the air conditioning system in FIG. 1, schematically;

[0035]FIG. 4 illustrates a perspective view of heat exchange means in apreheat exchanger in FIG. 3 in accordance with a preferred embodiment ofthe present invention;

[0036]FIG. 5 illustrates an air conditioning system of an improvedstructure in accordance with a first preferred embodiment of the presentinvention;

[0037]FIG. 6 illustrates a disassembled perspective view of an indoorunit in the air conditioning system in FIG. 5; and

[0038]FIG. 7 illustrates an air flow when the air conditioning system inFIG. 5 is in operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. In describing the embodiments, same parts will begiven the same names and reference symbols, and repetitive descriptionof which will be omitted.

[0040] The air conditioning system of the present invention provides aceiling type air conditioner in which an indoor unit is installed in aceiling. The air conditioning system of the present invention ventilatesroom air, during which the air supplied to a room recovers heat from theair discharged to an outside of room. The air conditioning system of thepresent invention will be described with reference to the attacheddrawings, in more detail. For reference, FIG. 1 illustrates an airconditioning system in accordance with a preferred embodiment of thepresent invention schematically, and FIG. 2 illustrates a view of theair conditioning system in FIG. 1 installed on a ceiling looked up frombelow.

[0041] Referring to FIG. 1, the indoor unit 5 is installed in theceiling of a room so as to be in communication with the room. The indoorunit 5 includes an indoor heat exchanger 5 a, an indoor expansion device(not shown), an indoor fan 5 b, and an air guide duct 5 c. The air guideduct 5 c has one end connected to an air supply duct 3 in communicationwith an outside of the room. Therefore, the indoor fan 5 b dischargesexternal air introduced into the indoor unit 5 through the air supplyduct 3 and the air guide duct 5 c to the room through the indoor heatexchanger 5 a and the air guide duct 5 c.

[0042] In the meantime, as shown in FIG. 2, there are a plurality of airdischarging ports 2 in the ceiling in the room at points predetermineddistances away from the indoor unit 5. As shown in FIG. 1, an airdischarge duct 4, connected to each of the air discharge ports 2, hasone end in communication with an outside of the room. Therefore, thepolluted air in the room is discharged to the outside of the roomthrough the air discharge port 2 and the air discharge duct 4. An airsupply fan 7 and an air discharge fan 8 are mounted on the air supplyduct 3 and the air discharge duct 4, respectively.

[0043] In the meantime, there is a preheat exchanger 6 in the middle ofthe air supply duct 3 and the air discharge duct 4, for the room air andthe external air flowing in the air supply duct 3 and the air dischargeduct 4 to cross each other and heat exchange indirectly. Therefore, theair conditioner of the present invention permits the external airsupplied to the room to recover heat from the air discharged to theoutside of room. The structure and operation of the preheat exchanger 6will be described with reference to FIGS. 3 and 4, in detail. Forreference, FIG. 3 illustrates heat exchange between external air androom air in the air conditioning system in FIG. 1 schematically, andFIG. 4 illustrates a perspective view of heat exchange means in apreheat exchanger in FIG. 3 in accordance with a preferred embodiment ofthe present invention.

[0044] Referring to FIG. 3, there is heat exchange means 6 a in thepreheat exchanger 6, including a plurality of guide passages 6 b forguiding the external air to the room, and a plurality of second guidepassages 6 c for guiding room air to the outside of the room. The firstguide passage 6 b is connected to the air supply duct 3, and the secondguide passage 6 c is connected to the air discharge duct 4. The firstguide passages 6 b and the second guide passages 6 c are separated witha plurality of plates, so as not to be in communication.

[0045] The first guide passage 6 b and the second guide passage 6 c areformed between the plates. Therefore, when the external air and the roomair respectively pass through the first guide passage 6 b and the secondguide passage 6 c, heat transfer is made through the plates.Accordingly, the external air introduced into the room through the firstguide passage 6 b receives heat from the room air discharged to theoutside of the room through the second guide passage 6 c. Therefore, theair conditioning system of the present invention can reduce energy lossin ventilation. In the meantime, the unexplained reference symbol 9denotes a filter, for filtering the air introduced into the room fromthe outside of the room.

[0046]FIG. 4 illustrates an embodiment of the heat exchange means 6 a.Referring to FIG. 4, the one embodiment of the heat exchange means 6 aincludes a plurality of plates 6 d and a plurality of flow guides 6 e.The plates 6 d are arranged at regular intervals such that the firstguide passage 6 b for flow of the external air and the second guidepassage 6 c for flow of the room air are formed in layers.

[0047] The flow guide 6 e serves to fix flow directions of the air flowin the first guide passage 6 b and the second guide passage 6 c, and tomake a heat exchanger area larger. The flow guide 6 e includes a sectionhaving a plurality of continuous folds, of which peaks and bottoms arein contact with a top surface and a bottom surface of each of theplates, respectively. In the meantime, as shown in FIG. 4, the flowguides 6 e in the layers may be arranged perpendicular to each other sothat the external air and the room air flow perpendicular to each other.

[0048] In the meantime, the heat exchange means is not limited to theembodiments described with reference to FIG. 4, but any structure isacceptable as the heat exchange means as far as the structure permitsindirect heat exchange of the external air and the room air withoutmixed to each other.

[0049] There can be two kind of methods for indirect heat exchangebetween the external air and the room air at the preheat exchanger 6.One is heat exchange by means of heat conduction made through the plate6 d and the flow guide 6 e that divide the first guide passage 6 b andthe second guide passage 6 c. The other one is heat exchange by means ofcondensed water formed on the plate 6 d due to a temperature differencebetween the first guide passage 6 b and the second guide passage 6 c.

[0050] In the meantime, in the air conditioning system in FIG. 1, theair supply fan 7 and the air discharge fan 8 are mounted on the airsupply duct 3 and the air discharge duct 4. The outdoor unit (not shown)in the outdoor includes an outdoor heat exchanger, a compressor, anoutdoor fan, which are generally known, and no more description of whichwill be given.

[0051] In the operation, referring to FIG. 1, when the outdoor unit andthe indoor unit 5 are put into operation, the room air is introducedinto the indoor unit 5, heat exchanges with the indoor heat exchanger,and discharged to the room, again. According to this, the room is cooledor heated. After the room is cooled or heated for a time period,ventilation is required, of which process will be described.

[0052] In the ventilation, the air discharge fan 8 and the air supplyfan 7 are operated. According to this, the external air is introducedinto the room through the air supply duct 3 and the air supply port 1,and the room air is discharged to the outside of the room through theair discharge duct 4 and the air discharge port 2. In this instance, theroom air and the external air flowing through the air discharge duct 4and the air supply duct 3 indirectly heat exchange at the preheatexchanger 6. Therefore, the external air receives a portion of thermalenergy from the room air discharged to the outside of the room, beforeintroduction into the room, according to which loss of thermal energycaused in the ventilation can be reduced.

[0053] The foregoing air conditioning system of the present inventionrecovers the thermal energy of the room air discharged to the outside ofroom with the air supplied to the room in ventilation. According tothis, rapid change of the room temperature in the ventilation can beprevented, and an energy saving effect can be obtained. However, despiteof the advantages, the air conditioning system described with referenceto FIGS. 1 and 3 has the following problems.

[0054] First, the air discharge duct in the ceiling in the room is longand complicate, to fail making the indoor unit compact, to be difficultto install, and to require much material and installation cost.

[0055] Second, there are a plurality of discharge ports mounted in theceiling, and the air discharge duct is connected to the ports. Accordingto this, since the air discharge duct is long, heat loss and pressureloss are occurred, that make the preheat exchange efficiency inventilation poor.

[0056] Therefore, an improved air conditioning system that can solve theforegoing problem is provided. FIGS. 5˜9 illustrate the improved airconditioning system in accordance with a first preferred embodiment ofthe present invention. The improved air conditioning system inaccordance with a first preferred embodiment of the present inventionwill be described with reference to above drawings.

[0057] Referring to FIG. 5, the indoor unit 10 is installed at one pointin the ceiling in the room so as to be in communication with the room.The indoor unit 10 has the air supply duct 20 and the air discharge duct30 connected thereto, respectively. Ends of the air supply duct 20 andthe air discharge duct 30 are mounted to be in communication with anoutside of room, respectively. In the middle of the air supply duct 20and the air discharge duct 30, there is preheat exchanger 40 forindirect heat exchange of the external air and the room air flowingtherethrough, respectively. A structure and function of the preheatexchanger 40, similar to one described with reference to FIGS. 3 and 4,will not be described, additionally.

[0058] In the meantime, though not shown, the outdoor unit is installedin an outdoor, which includes a compressor, an outdoor expansion device,and an outdoor fan. The outdoor unit, similar to known outdoor unit,will not be described, additionally. Of course, the outdoor unit and theindoor unit 10 are connected with refrigerant pipelines.

[0059] In the meantime, referring to FIGS. 5 and 6, the indoor unit 10includes an indoor heat exchanger 100, a fan 200, and a ventilation duct300. As shown in FIG. 5, the indoor heat exchanger 100 is mounted in anindoor unit case 11, and has a form with an inside space incommunication with the room. The indoor heat exchanger 100 may have aform, for an example, surrounding the space. In this case, the space maybe in communication with the room through an opened bottom side of theindoor heat exchanger 100. In the meantime, referring to FIG. 5, it ispreferable that an outside circumferential surface of the indoor heatexchanger 100 and an inside circumferential surface of the indoor unitcase has a fixed distance, for securing a discharge flow passage 15 sothat the air discharged from the fan and passed through the indoor heatexchanger 100 moves toward the room.

[0060] Referring to FIG. 5, the fan 200 is mounted in the space in theindoor heat exchanger 100. The fan 200 draws air, and discharges intothe room through the indoor heat exchanger 100. In the meantime, it ispreferable that the fan 200 provided to the air conditioning system inaccordance with a first preferred embodiment of the present inventionincludes a centrifugal fan that draws air from one side, for an example,from a bottom side, and discharges in a radial direction. In this case,referring to FIG. 5, the centrifugal fan is mounted in the inside spaceof the indoor heat exchanger 100, for drawing room air through thebottom side and discharges the room air in the radial direction. Then,the air discharged in the radial direction passes through the indoorheat exchanger 100 mounted to surround the centrifugal fan, and movestoward the room.

[0061] A ventilation guide duct 300 is mounted under the indoor heatexchanger 100, and has three flow passages for independent guide of theroom air, the external air, and the air passed through the indoor heatexchanger 100.

[0062] In this instance, the first flow passage guides fresh air fromthe outside of the room, and the room air to the fan 200. The first flowpassage has an upper part in communication with the space, and a lowerpart in communication with the room, and a part in communication withthe air supply duct 20.

[0063] A third flow passage, guiding the room air to the air dischargeduct 30, has a lower part in communication with the room, and a part incommunication with the air discharge duct 30. In this instance, thethird flow passage forms an independent flow passage from the first flowpassage with a partition wall 316.

[0064] A second flow passage guides the air passed through the fan 200and the indoor heat exchanger 100 to the room. There are a plurality ofsecond flow passages around the first flow passage and the third flowpassage, each having an upper part in communication with the dischargeflow passage 15 and a lower part in communication with the room.

[0065] In the meantime, referring to FIG. 6, one preferred embodiment ofthe ventilation guide duct having the first, second, and third flowpassages is shown. As shown in FIG. 6, the ventilation guide duct 300includes a duct body 310 and a panel 350. The duct body 310 is on anunderside of the indoor heat exchanger 100, and the panel 350 isattached to an underside of the duct body 310.

[0066] The duct body 310 has three holes forming parts of the first,second, and third flow passages, respectively. The first hole 311,passed through the duct body 310 in an up/down direction, forms a partof the first flow passage. Referring to FIG. 6, the first hole 311 is incommunication with the space and the air supply duct 20. As shown inFIG. 6, the third hole 313, passed through a part of the duct body 310in an up/down direction to form a part of the third flow passage, ismade independent from the first hole 311 by a partition wall 316. Thesecond hole 312, arranged around the first hole 311 and the third hole313 to pass through the duct body 310 in an up/down direction, forms apart of the second flow passage, and in communication with the dischargeflow passage 15.

[0067] When the duct body 310 has above structure, it is preferable thatthe fan 200 is provided over the first hole 311 and the third hole 313.It is also preferable that the indoor heat exchanger 100 stands on theduct body 310 along positions between the first hole 311 and the secondhole 312, and the first hole 311 and the third hole 313.

[0068] In the meantime, as described, the first, second, and third flowpassages in the duct body 310 may be the three holes passed through theduct body 310. In this case, the three holes may be provided in a formthe duct body 310 is machined to pass through the duct body 310, whenthe partition wall 316 is a part of the duct body 310 remained after themachining of the first hole 311 and the third hole 313.

[0069] However, as shown in FIG. 6, the first, second, and third flowpassages may be provided in a unique structure in which a plurality ofducts and plates of partition walls 316 are organically combined, whichwill be described hereafter.

[0070] Referring to FIG. 6, the duct body 310 includes a plurality offirst ducts 315, and the partition wall 316. Each of the first ducts 315has opened both ends, and an inside flow passage arranged in the up/downdirection. The plurality of the first ducts 315 surround a central partto form a cavity in the central part that is in communication with thespace and the room. The inside flow passages of the first ducts 315arranged as above provide the second holes 312 respectively, to form apart of the second flow passage.

[0071] The partition wall 316 divides the cavity into the first flowpassage and the third flow passage, i.e., the first hole 311 and thethird hole 313. As shown in FIG. 6, the partition wall 316 has oppositeends connected to opposite two first ducts 315. Therefore, as shown inFIG. 6, as the partition wall is mounted to cross a middle of the cavitysurrounded with the first ducts 315, the partition wall 316 divides thecavity into two flow passages. As shown in FIG. 6, such a partition wall316 can be mounted to divide the cavity into two flow passages havingthe same forms and sectional areas.

[0072] The partition wall 316 is mounted thus under the followingreason. The external air supplied to the first hole 311 through the airsupply ducts 20 is supplied to the room through the indoor heatexchanger 100 and the second hole 312 by the fan 200. At the same timewith this, polluted room air is introduced through the third hole 313,and discharged to the outside of the room through the air discharge duct30. In this instance, it there is no partition wall 316, a portion ofthe external air introduced into the first hole 311 through the airsupply duct 20 is introduced into the third hole 313, and drawn into theair discharge duct 30 directly. In this case, since a ventilationefficiency drops substantially, the present invention suggests mountingof the partition wall 316, for preventing the supplied external air frombeing discharged to the outside of the room directly through the airdischarge duct 30.

[0073] In the meantime, though not shown, the first ducts 315 may bearranged such that sides are connected to sides of the first ducts 315,or as shown in FIG. 6, spaced therefrom. In a case the first ducts 315are arranged in a state the sides of the first ducts 315 are connected,though not shown, the air discharge duct 30 can be arranged to passthrough a part of the first duct 315.

[0074] If the first ducts 315 are arranged in a state sides thereof arespaced a distance, the sides of the first ducts 315 arranged adjacent toeach other are connected with a connection plate 317 as shown in FIG. 6.In this case, the connection plate has a connection hole (not shown) forconnection to the air supply duct 20 or the air discharge duct 30.

[0075] As shown in FIG. 6, the panel 350 includes a first port 351 and asecond port 352. The first port 351 is provided to pass through acentral part of the panel 350 in an up/down direction to form parts ofthe first and third flow passages, i.e., so as to be in communicationwith the first hole 311 and the third hole 313, respectively. Therefore,the first flow passage is defined with the first hole 311 and the firstport 351, and the third flow passage is defined with the third hole 313and the first port 351. It is preferable that there is a mesh 355 formedat the first port 351 for filtering foreign matters since polluted roomair passes through the first port 351. In the meantime, though notshown, the second port 352 may be provided with a plurality of louvers(not shown) for guiding a discharge direction of the air passed throughthe indoor heat exchanger 100.

[0076] In the foregoing air conditioning system, an air supply fan 25and an air discharge fan 35 may be mounted on the air supply duct 20 andthe air discharge duct 30 respectively, for increasing airsupply/discharge capabilities.

[0077] In the meantime, in the air conditioning system of the presentinvention, though not shown, each of the air supply duct 20 and the airdischarge duct 30 may have at least one branch duct. In this case, thebranch ducts of the air supply duct 20 and the air discharge duct 30 arearranged to be in communication with the first and third flow passages.That is, FIG. 6 illustrates an embodiment in which the air supply duct20 and the air discharge duct 30 are provided to the first and thirdflow passages, wherein if the air supply duct and air discharge duct 20and 30 have the branch ducts respectively, the branch ducts can beconnected to the connection plates 317 shown in FIG. 6, respectively.

[0078] Thus, if the air supply and discharge ducts 20 and 30 have aplurality of branch ducts, flow rates of the external air and room airflowing through the first and third flow passages can be increased.Therefore, above structure is very useful in a site having a large spaceto require great air supply and discharge rates.

[0079] The operation of the air conditioning system having an improvedstructure in accordance with the first preferred embodiment of thepresent invention will be described. When the fan is put into operationin a state the air supply fan 25 and the air discharge fan 35 are not inoperation, the room air moves upward through the first hole 311 and thethird hole 313 in the ventilation guide duct 300, and is dischargedtoward the indoor heat exchanger 100 by the fan. The air cooleddown/heated up as the air heat exchanges at the indoor heat exchanger100 is discharged to the room via the discharge flow passage 15, thesecond hole 312, and the second port 352, to cool down/heat up the room.In the meantime, in a state the air supply fan 25 and the air dischargefan 35 are not in operation, since air flow in the air supply duct 20and the air discharge duct 30 are minimal, it is difficult to make anefficient ventilation.

[0080] In a case it is intended to ventilates the room after the room iscooled or heated for a preset time period through the foregoing process,the air supply fan 25 and the air discharge fan 35 are put intooperation. In this instance, the outdoor unit and the indoor unit 10 maybe put into operation at the same time, or may not put into operation. Acase when the outdoor unit and the indoor unit 10 are put into operationwill be described, as an example.

[0081] When the air supply fan 25 is put into operation, fresh externalair is introduced into the air supply duct 20, and passes through, andreceives a thermal energy from the room air at, the preheat exchanger40. A heat transfer process taken place at the preheat exchanger 40 isthe same as described before. The external air passed through thepreheat exchanger 40 is introduced into the first hole 311 in theventilation guide duct 300 through the air supply duct 20 or a branchduct thereof. The external air introduced into the first hole 311 isblown toward the indoor heat exchanger 100 by the fan 200, and heatexchanges at the indoor heat exchanger 100. The external air heated orcooled at the indoor heat exchanger 100 is discharged to the roomthrough the discharge flow passage 15 and the second flow passage of theventilation guide duct 300, i.e., the second hole 312 and the secondport 352. In the meantime, a portion of the room air moves toward thefan 200 through the third hole 313, and discharged to the room againthrough the indoor heat exchanger 100.

[0082] Thus, in ventilation, the air conditioning system heats or coolsthe fresh air introduced from the outside of the room at the preheatexchanger 40 primarily, and heats or cools at the indoor heat exchanger100 secondarily, before supply to the room. Therefore, even in theventilation, cooled or heated air required according to a roomenvironment is supplied, the sharp room temperature change can beprevented in the ventilation. Moreover, since the external air suppliedto the room recovers the thermal energy from the discharge room air, anenergy loss can be reduced.

[0083] In the meantime, when the discharge fan 35 is put into operation,the room air is introduced into the air discharge duct 30 through thefirst port 351 and the third hole 313. In this instance, the partitionwall 316 provided to the ventilation guide duct 300 prevents theexternal air introduced through the first hole from the air supply duct20 from being introduced into the air discharge duct 30, directly. Theroom air introduced into the air discharge duct 30 passes through, andheat exchanges with the external air indirectly at, the preheatexchanger 40. In this time, the thermal energy of the room air istransferred to the external air. The room air passed through the preheatexchanger 40 is discharged to the outside of the room in a cooled orheated state.

[0084] Advantages of the improved air conditioning system in accordancewith a preferred embodiment of the present invention will be described.

[0085] First, in ventilation, the air conditioning system of the presentinvention has the preheat exchanger to transfer the thermal energy ofroom air discharged to the outside of the room to the external airsupplied to the room. According to this, waste of the thermal energyduring ventilation can be prevented, effectively.

[0086] Second, in ventilation, the external air cooled or heatedprimarily at the preheat exchanger is cooled or heated again as theexternal air passes through the indoor heat exchanger, before beingsupplied to the room. Therefore, the sharp room temperature change inthe ventilation can be prevented effectively. According to this, acomfortable environment can be provided to persons in the room.

[0087] Third, the air conditioning system of the present invention hasthe indoor heat exchanger, the indoor fan, the ventilation guide duct,which form an indoor unit assembly. Therefore, the indoor unit is verycompact, permitting easy installation of the indoor unit in the ceiling.

[0088] Fourth, the air conditioning system of the present invention candispense with the air supply ports or the air discharge ports mounted inthe ceiling. Accordingly, a number of ducts are fewer, and a totallength of the ducts is shorter. Therefore, installation is easy, andmaterial and fabrication costs can be reduced. Moreover, heat loss andpressure loss occurred at the ducts can be reduced, to improve an airconditioning efficiency.

[0089] Fifth, since the air conditioning system of the present inventioncan dispense with separate air discharge ports, a room interior looksbetter.

[0090] Sixth, a design change is very easy, in which an air supply rateand an air discharge rate are provided differently.

[0091] Seventh, the partition wall separates flow passages of the roomair and the external air. Thus, only with very simple element, astructure can be provided, in which ventilation efficiency can beincreased, and energy consumption can be reduced.

[0092] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An air conditioning system comprising: an outdoor unit having a compressor and an outdoor heat exchanger; an indoor unit installed in a ceiling, having an indoor heat exchanger with a space therein in communication with a room, a fan in the space for drawing air and discharging through the indoor heat exchanger, and a ventilation guide duct on an underside of the indoor heat exchanger having a partition wall for separating external air supplied from an outside of the room, and room air, for guiding the external air to the room through the fan, and the room air to the outside of the room; an air supply duct and an air discharge duct each having one end connected to the ventilation guide duct for guiding the external air to the room, and the room air to the outside of the room, respectively; and a preheat exchanger provided in the middle of the air supply duct and the air discharge duct, for indirect heat exchange of the external air and the room air passing through the air supply duct and the air discharge duct.
 2. The air conditioning system as claimed in claim 1, wherein the fan includes a centrifugal fan that draws air from under and discharges in a radial direction as the fan rotates.
 3. The air conditioning system as claimed in claim 1, wherein the ventilation guide duct includes; a first flow passage in communication with the space, the room, and the air supply duct, for guiding the room air and the external air to the fan, at least one or more than one second flow passage for guiding the air passed through the fan and the indoor heat exchanger to the room, and a third flow passage for guiding the room air to the air discharge duct.
 4. The air conditioning system as claimed in claim 3, wherein the ventilation guide duct includes; a duct body on an underside of the indoor heat exchanger, and a panel attached to an underside of the duct body.
 5. The air conditioning system as claimed in claim 4, wherein the duct body includes; a first hole passed in an up/down direction to form a part of the first flow passage and in communication with the air supply duct, a third hole passed in the up/down direction to form a part of the third flow passage, in communication with the air discharge duct, and made independent from the first hole by the partition wall, and a second hole passed in the up/down direction to form a part of the second flow passage.
 6. The air conditioning system as claimed in claim 4, wherein the duct body includes; first ducts arranged to surround a central part to form a cavity in the central part that is in communication with the space and the room, each of the first ducts having an inside forming a part of the second flow passage, and the partition wall arranged to divide the cavity into the first flow passage and the third flow passage.
 7. The air conditioning system as claimed in claim 6, wherein the partition wall has opposite two ends connected to opposite first ducts.
 8. The air conditioning system as claimed in claim 6, wherein the partition wall divides the cavity into two flow passages having the same forms and sectional areas.
 9. The air conditioning system as claimed in claim 6, wherein the duct body further includes connection plates connected between side ends of adjacent first ducts, and the air supply duct or the air discharge duct is connected thereto selectively.
 10. The air conditioning system as claimed in claim 4, wherein the panel includes; a first port formed to form parts of the first and third flow passages, respectively, and a second port formed to form a part of the second flow passage.
 11. The air conditioning system as claimed in claim 10, wherein the panel further, includes a mesh provided to the first port.
 12. The air conditioning system as claimed in claim 10, wherein the panel further includes a plurality of louvers provided to the second port for guiding a discharge direction of the air passed through the indoor heat exchanger.
 13. The air conditioning system as claimed in claim 5, wherein the fan is provided over the first hole and the third hole.
 14. The air conditioning system as claimed in claim 5, wherein the indoor heat exchanger stands on the duct body along positions between the first hole and the second hole, and the first hole and the third hole.
 15. The air conditioning system as claimed in claim 1, wherein the preheat exchanger includes; first guide passages arranged at regular intervals for flow of the external air therethrough, and second guide passages arranged to be in contact between the first guide passages for flow of the room air therethrough.
 16. The air conditioning system as claimed in claim 1, wherein the preheat exchanger includes; a plurality of plates arranged at regular intervals so that the first guide passages for flow of the external air and the second guide passages for flow of the room air are formed in layers, and a plurality of flow guides provided between the plates for each of the layers in parallel to flow directions of the external air and the room air respectively, each having a cross section with a plurality of continuous folds.
 17. The air conditioning system as claimed in claim 16, wherein the fold includes a perk and a bottom in contact with a top surface and a bottom surface of the plates.
 18. The air conditioning system as claimed in claim 16, wherein the flow guides in each of the layers are arranged perpendicular to each other such that the external air and the room air flow in perpendicular to each other.
 19. The air conditioning system as claimed in claim 1, further comprising an air supply fan mounted on the air supply duct for supplying the external air to the room.
 20. The air conditioning system as claimed in claim 1, further comprising an air discharge fan mounted on the air discharge duct for discharging the room air to the outside of the room.
 21. The air conditioning system as claimed in claim 3, wherein the air supply duct and the air discharge duct include at least one or more than one branch ducts branched from one ends thereof and connected to the first flow passage and the third flow passage. 